Electric motor based holding control systems and methods

ABSTRACT

A holding system includes a force control module configured to generate a force signal to cause a holding device to perform at least one of a hold stroke and a release stroke. The hold stroke includes transitioning a gripping element of the holding device to a first position to grip an object. The release stroke includes transitioning the gripping element to a second position to release the object. The holding device is non-backdrivable. A stall detection module is configured to (i) monitor a sensor signal received from a sensor of an electric motor assembly of the holding device and (ii) detect a first stall condition of an electric motor based on the sensor signal. A shut off module is configured to shut off current to the electric motor based on the detection of the first stall condition during or at an end of the release stroke.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/525,436, filed Jun. 8, 2012, which claims priority to U.S. patentapplication Ser. No. 61/501,418, filed Jun. 27, 2011. The entiredisclosures of the above applications is are incorporated herein byreference.

FIELD

The present disclosure relates to holding control systems, and moreparticularly to control systems for electrically actuated holdingdevices, such as grippers and clamps.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Various holding systems are used in manufacturing to hold and/or moveobjects between locations. Example holding systems are gripper systemsand work holding systems or systems that include clamps. Gripper systemsare typically used for gripping and/or moving objects between locations.A gripping procedure may include four steps. During a first step, agripper is closed to grip an object at a first location. During a secondstep, an external device (or actuator) moves the gripper from the firstlocation to a second location. During a third step, the object isreleased from the gripper at the second location. During a fourth step,the external device moves the gripper back to the first location to pickup another object.

Work holding systems typically include one or more clamps that areactuated to hold a part. Each clamp may have, for example a hold stateand a release state. During the hold state the clamp is actuated to andheld in a part holding position. This prevents the part from movingrelative to a fixture. During the release state the clamp is actuated toa backoff (or non-holding) position. This allows the part to be removedfrom the fixture.

Holding systems may be pneumatic-based or electric-based. Thepneumatic-based holding systems include a pneumatic circuit. Thepneumatic circuit may include a body and pneumatically actuated valves.The valves are opened and closed to adjust a pressure within a cylinderof the body. A piston is translated within the cylinder based on thepressure in the cylinder. Movement of the piston causes holdingelement(s) (e.g., gripper fingers or a clamp arm) to hold or release anobject. In a gripper implementation, the gripper fingers may be in aclosed (gripping) state or an open (release) state. In a clampimplementation, the clamp arm may be in a hold state or a release state.Sensors may be used to detect the state of the holding elements bymonitoring position of the piston within the cylinder and/or by directlydetecting position of the holding elements.

As a first example, the piston may include magnets, which may bedetected via sensors externally mounted on the body. The body mayinclude a groove that extends parallel to the direction of motion of thepiston. Magneto-resistive sensors may be mounted on the body over thegroove and detect movement of the magnets (i.e. movement of the piston).These sensors may be used to generate, for example, OPEN and CLOSEsignals or HOLD and RELEASE signals for automation control. The signalsindicate whether the holding elements are in the open, closed, holdand/or release states. As another example, externally mounted inductivesensors may be used to sense holding element movement (e.g., gripper jawand/or finger movement).

Use of the externally mounted sensors has associated disadvantages. Inaddition to cost of the sensors and associated cables, the cables candegrade due to, for example, iterative cycling through a gripperprocedure. Since a gripper is iteratively moved between locations,certain points on the cables can wear out and thus prevent use of thegripper. In addition, manual adjustments may be needed to swap outsensors on a holding system to accommodate objects of different size.Each object may have a respective set of associated sensors.

Electric-based holding systems may include one or more electric motorsmounted on a body. The electric motor(s) are used to actuate holdingelements. Sensors may be mounted on the body to detect state of theholding device. Similar issues can arise with these sensors as with thesensors of the pneumatic-based holding systems.

In addition, electric current supplied to the electric motor(s) may needto be maintained or adjusted in order to maintain a desired pressure onan object when holding elements are in a closed or hold state. A typicalstepper motor may need to remain on (drawing full power) regardless ofthe location or movement of the holding elements. This can result in theelectric motors being operated at increased temperatures for extendedperiods of time, which can limit maximum output torque levels of theelectric motors and/or degrade and reduce operating life of componentsof the electric motors. Also, as current is maintained, powerconsumption is increased.

SUMMARY

A holding system is provided and includes a force control moduleconfigured to generate a force signal to cause a holding device toperform at least one of a hold stroke and a release stroke. The holdstroke includes transitioning a gripping element of the holding deviceto a first position to grip an object. The release stroke includestransitioning the gripping element to a second position to release theobject. The holding device is non-backdrivable. A stall detection moduleis configured to (i) monitor a sensor signal received from a sensor ofan electric motor assembly of the holding device and (ii) detect a firststall condition of an electric motor based on the sensor signal. A shutoff module is configured to shut off current to the electric motor basedon the detection of the first stall condition during or at an end of therelease stroke.

In other features, a holding system is provided and includes a forcecontrol module configured to generate a force signal to cause a holdingdevice to perform at least one of a hold stroke and a release stroke. Astall detection module is configured to (i) monitor a sensor signalreceived from a sensor of an electric motor assembly and (ii) detect astall condition of an electric motor based on the sensor signal. Aboosting module is configured to increase current to the electric motorto a boost current level and unbind a leadscrew of the electric motorassembly. The boost current level is greater than an applied currentlevel. The applied current level is used to transition a grippingelement of the holding device between a hold state and a release state.The boosting module, when boosting the current, is configured to adjustthe force signal based on a direction of travel of the electric motorand the sensor signal.

In other features, a holding system is provided and includes a forcecontrol module configured to generate a force signal to cause a holdingdevice to perform a release stroke. A gripping element of the holdingdevice is actuated to release an object when the release stroke isperformed. A stall detection module is configured to (i) monitor asensor signal received from a sensor of an electric motor assembly and(ii) detect a stall condition of an electric motor based on the sensorsignal. An end-of-travel module is configured to move the grippingelement of the holding device away from a hard stop a predetermineddistance including adjusting the force signal based on the detection ofthe stall condition.

In other features, a holding system is provided and includes a forcecontrol module configured to generate a first force signal to cause aholding device to perform at least one of a hold stroke and a releasestroke. A stall detection module is configured to (i) monitor a sensorsignal received from a sensor of an electric motor assembly and (ii)detect a stall condition of an electric motor based on the sensor signalat an end of the hold stroke or the release stroke. The force controlmodule is configured to adjust the force signal to reduce current to theelectric motor from a first current level to a second current levelbased on detection of the stall condition and while the holding deviceis holding an object. The second current level is greater than a minimumcurrent level for holding the object.

In other features, a torque method of a holding device is provided. Themethod includes: determining a minimum output torque and a maximumoutput torque of a motor of the holding device; assigning a maximumvoltage to the minimum output torque; assigning a minimum voltage to themaximum output torque; interpolating output torques between the minimumoutput torque and the maximum output toque based on the minimum voltageand the maximum voltage; operating the holding device in an appliedtorque mode based on the interpolated output torques, wherein theholding device is performing one of a hold stroke and a release strokewhen in the applied torque mode; and providing the motor with theminimum voltage when operating in a hold mode, wherein during the holdmode the holding device is in a stall condition.

In other features, a holding system is provided and includes a holdingdevice control module configured to (i) provide a power output and (ii)generate an open signal, a close signal, and a force signal. The forcesignal indicates a requested output torque of an electric motor. A motorcontrol module is configured to generate feedback signals indicating astall condition of the holding device. The feedback signals aregenerated by a sensor mounted within a housing of the electric motor.The holding system further includes a cable assembly. The cable systemincludes a first connector configured to connect to the holding devicecontrol module via a cable. The cable is connected between the holdingdevice control module and the cable assembly. A second connector isconnected to the motor control module and provides the open signal andthe close signal from the holding device control module to the motorcontrol module. The second connector provides the feedback signals fromthe motor control module to the holding device control module. A thirdconnector is connected to the motor control module and providing thepower output or the force signal from the holding device control moduleto the motor control module. Signal lines, separate from the cable, areconnected between the (i) first connector and (ii) at least one of thesecond connector and the third connector.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an electric-based holding systemin accordance with the present disclosure;

FIG. 2 is a cross-sectional view of a gripper in accordance with thepresent disclosure;

FIG. 3 illustrates a motor shut off method in accordance with thepresent disclosure;

FIG. 4 illustrates a boosting method in accordance with the presentdisclosure;

FIG. 5 is a torque plot illustrating a boost mode in accordance with thepresent disclosure;

FIG. 6 is a diagram illustrating an end-of-travel routine andcorresponding gripper finger states in accordance with the presentdisclosure;

FIG. 7 illustrates an end-of-travel method in accordance with thepresent disclosure;

FIG. 8 is a torque plot illustrating a hold mode in accordance with thepresent disclosure;

FIG. 9 illustrates a gripping method in accordance with the presentdisclosure;

FIG. 10 is a force versus voltage graph of a transfer function inaccordance with the present disclosure;

FIG. 11 illustrates a torque method in accordance with the presentdisclosure;

FIG. 12A is a perspective view of a cable assembly in accordance withthe present disclosure;

FIG. 12B includes perspective views and pin outs of connectors of thecable assembly of FIG. 12A;

FIG. 12C is a front view and pin out of a connector of the cableassembly of FIG. 12A;

FIG. 13 is a cross-sectional view of a clamp in a release state and inaccordance with the present disclosure;

FIG. 14 is a cross-sectional view of the clamp of FIG. 13 in a holdstate;

FIG. 15 is a torque plot illustrating a move mode in accordance with thepresent disclosure;

FIG. 16 is a torque plot illustrating multiple applied modes inaccordance with the present disclosure; and

FIG. 17 illustrates another gripping method in accordance with thepresent disclosure.

DETAILED DESCRIPTION

In the following description, grippers are primarily described asgripping an object when in a closed state and releasing an object whentransitioning from a closed state to an open state. In certain gripperapplications a gripper may grip an object when in an open state andrelease an object when transitioning from an open state to a closedstate. Thus, the following described implementations may also be appliedto grippers that grip an object when in an open state.

In FIG. 1, an electric-based holding system (“holding system”) 10 isshown and includes a holding device control module 12, a motor assembly13 with a motor control module 14 and an electric motor 15, and aholding device 16. The holding system 10 may be referred to, forexample, as a gripper system or a clamp system. The holding device 16may be, for example, a gripper or a clamp having one or more grippingelement(s). The holding device control module 12 is connected to themotor assembly 13 via a flex cable 17. The flex cable 17 includes afirst connector 18 that is connected to a second connector 19 on themotor assembly 13. The second connector 19 is part of a cable assembly20, which is internal to the motor assembly 13. The cable assembly 20simplifies an interface between the holding device control module 12 andthe motor control module 14. The configuration of the flex cable 17 andthe cable assembly 20 provides ease in connecting the holding devicecontrol module 12 to the motor control module 14.

The flex cable 17 may be highly flexible. As an example, the flex cable17 may have a bending radius of less than or equal to 15 times the outerdiameter (OD) of the flex cable 17 (or 15×OD). In one implementation,the bending radius of the flex cable 17 is 10×OD. The bending radius maybe determined at any point along the cable. The high flexibility of theflex cable 17 prevents breakdown of the cable 149 during use. The flexcable 17 may have a bending cycle life of, for example, greater than orequal to 20 million cycles. Although not shown in FIGS. 12A-12C, theflex cable 17 may include a center core, chords, a sheath, a groundshield, etc. The flex cable 17 may include thermoplastic elastomer(TPE), polyurethane (PUR), polytetrafluoroethylene (PTFE) and/or nylonto provide flexibility, abrasion resistance and resistance to hydraulicfluids and hydrocarbons. Conductors of the flex cable 17 may be formedof, for example, gold (Au), nickel (Ni), brass, copper (Cu), zinc (Zn)and/or other electrically conductive materials.

The holding device control module 12 may be a programmable logiccontroller (PLC) and commands OPEN and CLOSE or HOLD and RELEASE statesof the holding device 16. The motor control module 14 controls operationof the electric motor based on power and discrete input and output (I/O)control signals from the holding device control module 12. The motorcontrol module 14 may be programmable and may include a shut off module21, a boosting module 22, an end-of-travel module 23, a hold module 24,a stall detection module 26 and a force control module 28. The modules21-28 are provided as an example, one or more of the modules 21-28 maybe combined in a single module or excluded from the motor control module14. For example, the force control module 28 may include the shut off,boosting and/or hold modules 21, 22, 24. The motor control module 14 mayalso include a memory 29 for storing various software algorithms androutines, predetermined values, thresholds, set points, voltages,current values, etc. disclosed below.

The cable assembly 20 includes the second connector 19, a first set ofwires 30, a second set of wires 31, a third connector 32, and a fourthconnector 33. The first set of wires 30 is connected between the secondconnector 19 and the third connector 32. The second set of wires 31 isconnected between the second connector 19 and the fourth connector 33.The third connector 32 is connected to a fifth connector 34 on the motorcontrol module 14. The fifth connector 34 may be connected to the motorcontrol module 14 as shown or may be connected to directly to theelectric motor 15. The fourth connector 33 is connected to a sixthconnector 35 on the motor control module 14.

Operation of each of the modules 14 and 21-28 is described in detailbelow with respect to FIGS. 2-14. Examples of the holding device 16 areshown in FIGS. 2, 13 and 14 and an example of the cable assembly 20 isshown in FIGS. 12A-12C. Although the following implementations of FIGS.2-11 are primarily described with respect to a gripper, theimplementations may be modified and/or applied to other holding devices.An example of another holding device is provided in FIGS. 13 and 14.

Referring now also to FIG. 2, a holding device 16′ is shown. The holdingdevice 16′ is a gripper and includes a motor stand 36, a gripper body37, and fingers (or gripping elements) 38. An electric motor assembly(“the motor”) 39 is mounted on the motor stand 36 and drives a coupling41 to move a wedge 42 in the gripper body 37. The motor 39 includes themotor control module 14 and the electric motor 15, which are mountedwithin a housing 52 of the motor 39. A combination of the motor 39 andthe gripper body 37 may be referred to as a linear actuator. Translationof the wedge 42 moves the fingers 38 between open and closed states. Themotor 39 may include a leadscrew 50 that is driven in and out of thehousing 52 of the motor 39 via a rotor (or motor) nut 54. The leadscrew50 does not rotate and the rotor nut 54 rotates in a fixed positionrelative to the housing 52.

The direction of travel of the leadscrew 50 is based on the rotatingdirection of the rotor nut 54. Driving the leadscrew 50 into the housing52 causes the coupling 41 to pull the wedge 42 in an inward directionand toward the electric motor 15 thereby causing the finger 38 to moveto a closed state, as shown. The fingers 38 may be in a fully open statewhen the leadscrew 50 is driven out of the housing 52.

The motor 39 may include one or more internal sensors (not shown) fordetecting position of the leadscrew 50, which indicates position of thefingers 38. As an example, the motor 39 may include an encoder or othersensors (not shown) that detects position of the leadscrew 50. Theencoder and/or internal sensors may be monitored by the stall detectionmodule 26 and provide feedback (e.g., position information) indicatingwhether the fingers 38 are in an OPEN or a CLOSED state. The motorcontrol module 14 and/or the stall detection module 26 may generate OPENSENSE and CLOSE SENSE signals, which indicate the OPEN and CLOSED statesand are provided on OPEN SENSE and CLOSE SENSE lines (examples of whichare shown in FIGS. 12A-12C). The OPEN and CLOSE states and the OPENSENSE and CLOSE SENSE signals lines may refer to HOLD and RELEASE statesand/or HOLD SENSE and RELEASE SENSE signal lines. The OPEN and CLOSEDstates may be based on whether the leadscrew 50 is at a hard stop. Ahard stop refers to when the fingers 38 are against an object and are nolonger moving and/or when, for example, components of the motor 39(e.g., the leadscrew 50, the coupling 41 and/or the wedge 42) havereached a travel limit. This may occur, for example, when the fingers 38have closed or opened and gripped an object or when the fingers 38 havemoved to an end-of-travel limit.

The implementations described herein with respect to the modules 14 and21-28 may be applied to electric motors of various types. As such, theelectric motor 15 may be of various types. As a couple of examples, theelectric motor 15 may be a rotary motor or a linear motor. The electricmotor 15 may be a stepper motor, a brush motor, a brushless motor, etc.As a further example, the electric motor 15 may be an anti-stall steppermotor.

Internal Sensor Simulation

Traditional pneumatic and/or electric based grippers typically includeexternally mounted sensors for detecting open and close positions of thegrippers. Externally mounted sensors refer to sensors mounted on a bodyof a gripper system external to a motor and/or a motor housing. Use ofexternally mounted sensors has associated disadvantages. Stall detectionmethods described herein can be used to detect open and closed states ofa gripper without the use of externally mounted sensors.

A stall condition may result when the leadscrew 50 has reached a hardstop. A stall condition refers to when power is provided to translatethe leadscrew 50, but the leadscrew 50 is not moving due to the hardstop preventing further movement. The motor control module 14 and/orstall detection module 26 may detect stalled conditions and indicatethis via the OPEN and CLOSE (or HOLD and RELEASE) SENSE signal lines. Inone implementation, the stall detection module 26 detects the stalledconditions and may generate a stall signal and/or sets a stall flag,which may be stored in the memory 29. The motor control module 14 maygenerate the OPEN SENSE and CLOSE SENSE signals based on the stallsignal and/or set flag.

The stalled conditions may be detected based on current and/or voltageapplied to the electric motor 15, a direction of travel of the fingers38, signals from an encoder, and/or signals from internal sensor(s). Theinternal sensors may be disposed within the motor housing 52. As anexample, the stalled conditions may be detected by sensing positionsand/or rotation of an encoder mounted internal to the motor housing 52.The OPEN and CLOSE SENSE signal lines may provide digital and/orHIGH/LOW sensor signals indicating whether the holding device 16′ isstalled and is in an open or closed state.

The OPEN and CLOSE SENSE signals may be provided on output pins of thesecond connector 19 and detected by the holding device control module12. The OPEN and CLOSE SENSE signals can be used to simulate and/orprovide information typically provided by normally open or normallyclosed externally mounted sensors (e.g., PNP or NPN transistor basedsensors). This removes the need for external sensors and resolves issuesassociated therewith.

Backdrivable Versus Non-Backdrivable

The linear actuator, the holding device 16 and/or the leadscrew 50 maybe backdrivable or non-backdrivable based on the pitch of the leadscrew50. The linear actuator, the holding device 16 and/or the leadscrew 50are backdrivable when power to the electric motor 15 is shut off (orremoved) and the leadscrew 50 moves due to pressures between the fingers38 and an object being held by the fingers 38. Pitch of the leadscrew 50may be based on the gripper application of use. The pitch of theleadscrew 50 refers to the number of threads per predetermined length ofthe leadscrew 50. A fine leadscrew has more threads per predeterminedlength than a coarse leadscrew. A fine leadscrew may not be backdrivabledue to the forces required to overcome friction between, for example,the leadscrew and the rotor nut 54. A coarse leadscrew may bebackdrivable, as the forces required to overcome friction are less.

Motor Shut Off

In a gripper application that includes the use of a fine leadscrew, theshut off module 21 may shut off power to the electric motor 15 toconserve energy. For example, the power to the electric motor 15 may beremoved when the holding device 16′ has gripped an object and/or hasreached a hard stop.

As a fine leadscrew is non-backdrivable, power may be removed whilemaintaining a desired grip (or hold) force on the object. A leadscrewwith a desired pitch may be selected based on a rated force level. Therated force level refers to the force to hold an object plus a safetymargin. As a result, the force to overcome friction and backdrive theselected leadscrew is more than the force to hold the object. Thisenables failsafe operation by preventing an object from being droppedwhen power is removed. In addition to removing power to the electricmotor 15, power may also be partially or fully removed from the holdingdevice control module 12 and/or the motor control module 14.

As an example, the shut off module 21 shuts off power to the holdingdevice control module 12, the electric motor 15, and/or the motorcontrol module 14 when the motor 39 completes an Open, Close, Holdand/or Release transitional movement (or stroke). Grip force ismaintained since the selected leadscrew is non-backdrivable. The shutoff module 21 may implement a stall detection routine to detect when toshut off the power. The shut off module 21 may receive and continuouslymonitor the OPEN SENSE signal, the CLOSE SENSE signal and/or othersignals from the motor 39 (or encoder and/or other internal sensors)when a command has been issued to transition between the OPEN and CLOSEDstates. The OPEN and CLOSE SENSE signals are generated independent ofstroke position (i.e. positions of the fingers 38).

The shut off module 21 may detect a stall condition based on the OPENand CLOSE SENSE signals and start a counter. If the counter reaches apredetermined threshold, a flag is set that enables execution of a motorshut off routine. The motor shut off routine may shut off current and/orvoltage to the electric motor 15 and/or other elements of the holdingsystem 10. The shut off module 21 may shut off power to the motor 39and/or the electric motor 15 by removing power to POWER and/or POWER I/Opins of the motor 39. These pins are shown in FIGS. 12B-12C. Thebackdrivable leadscrew maintains force and position of fingers 38 whenthe power is off.

A gripping process may include 4 steps. The 4 steps include: 1) grippingan object (i.e. closing or opening gripper fingers) at a first location;2) moving the gripper from a first location to a second location; 3)releasing the object (i.e. performing the opposite motion with thegripper fingers as in step 2); and 4) moving the gripper back to thefirst location to pick up a next object. With the motor shut off routineenabled, the shut off module 21 may shut off power to the electric motor15 and/or other elements of the holding system 10 for a duration of the2^(nd) and 4^(th) steps. This can reduce energy consumption and heatgeneration by as much as 50% (relative to an electric-based grippersystem without motor shut off control) when durations of each of the 4steps are equal in length. As a result, less energy is consumed duringeach cycle of the gripping process while heat generation is reduced.Reduced heat generation allows a motor to be driven harder (commanded tooutput larger torque levels for increased periods of time). With lesspower consumed, the holding system 10 is cheaper to operate relative totraditional holding systems and allows for increased output torque (orgripping forces) to be generated.

The holding system 10 may be operated using numerous methods, examplemethods are provided by the methods of FIGS. 3, 5, 7, 9, 11 and 17. Thebelow-described tasks of FIGS. 3, 5, 7, 9, 11 and 17 are meant to beillustrative examples; the tasks may be performed sequentially,synchronously, simultaneously, continuously, during overlapping timeperiods or in a different order depending upon the application. Also,any of the tasks may not be performed or skipped depending on theimplementation and/or sequence of events.

In FIG. 3, a motor shut off method is shown. Although the followingtasks are primarily described with respect to the implementations ofFIGS. 1-2, the tasks may be easily modified to apply to otherimplementations of the present disclosure. The tasks may be iterativelyperformed. The method may begin at 60.

At 62, the motor control module 14 transitions gripping elements of agripper to an OPEN or CLOSED state to grip an object at a firstlocation. This includes performing a hold stroke. At 64, the shut offmodule 21 monitors the OPEN and CLOSE SENSE signals and detects a stallcondition at an end of the hold stroke.

At 66, the shut off module 21 starts a counter. At 67, the shut offmodule 21 determines whether the counter has reached the predeterminedthreshold. If the threshold is reached, task 68 is performed. At 68, theshut off module 21 shuts off current and/or voltage to the electricmotor 15.

At 70, the gripper including motor assembly 13 are moved from a firstlocation to a second location. This includes the shut off module 21turning on and/or permitting the electric motor 15 to be turned on. At72, the motor control module 14 transitions the gripping elements from ahold state to a release state by performing a release stroke.

At 74, the shut off module 21 monitors the OPEN and CLOSE SENSE signalsand detects a stall condition at an end of the release stroke.

At 76, the shut off module 21 resets and starts the counter. At 78, theshut off module 21 determines whether the counter has reached thepredetermined threshold. If the threshold is reached, task 80 isperformed. At 80, the shut off module 21 shuts off current and/orvoltage to the electric motor 15.

At 82, the gripper including the motor assembly 13 is moved from thesecond location to the first location. The method may end at 83 or mayreturn to task 60.

Motor Boosting

A binding situation can occur under certain conditions when anon-backdrivable leadscrew is used. Binding refers to when a leadscrew(e.g., the leadscrew 50) binds (becomes stuck together) with a nut of anelectric motor (e.g., the rotor nut 54). This can occur when the linearactuator is driven into a hard stop, which stalls the electric motor 15.In this scenario, a torque mode algorithm is used to sense the stalledmotor and apply a motor control signal to generate a predeterminedamount of output torque. The torque mode algorithm may be executed by,for example, the force control module 28. The output torque is producedto provide an adequate level of pressing force on the object by thefingers 38 thereby holding the object when at a hard stop. This allowsthe motor 39, in addition to being used for positioning an object, toalso be used for holding an object when at a hard stop.

The rotor of the motor 39 is static (i.e. stationary) when the motorcontrol module 14 (or force control module 28) commands the outputtorque to continue pressing on a hard stop. A force signal FORCE may beoriginally supplied from the holding device control module 12 to themotor control module 14. The motor control module 14 may adjust thecurrent received by the electric motor 15 based on the force signalFORCE. The continued pressing action causes the leadscrew 50 and therotor nut 54 to be wedged into or against the hard stop. As a result,the leadscrew 50 binds with the rotor nut 54.

The longer the leadscrew 50 and the rotor nut 54 are in a binded state,the more force needed to break free the leadscrew 50 and/or the rotornut 54. The leadscrew 50 and the rotor nut 54 may remain in a bindedstate for extended periods of time, for example, when the holding device16′ is driven to a fully closed or open position during assembly andremains in that state until used by a customer. If the holding device16′ is actuated immediately after being driven into a binded (or wedged)state, the tendency for the leadscrew 50 and the rotor nut 54 stayingbound is virtually non-existent.

Referring now also to FIG. 4, a boosting method is shown. The boostingmodule 22 may boost output torque of the electric motor 15 during aboost mode to unbind the leadscrew 50 and/or the rotor nut 54. Althoughthe following tasks are primarily described with respect to theimplementations of FIGS. 1-2, the tasks may be easily modified to applyto other implementations of the present disclosure. The tasks may beiteratively performed. The method may begin at 90.

At 92, the stall detection module 26 determines that the leadscrew 50 isin a binded stated against a hard stop, as described herein. At 94, theboosting module 22 initiates a boost routine when initially signalingthe electric motor 15 to move the fingers 38 (or gripping elements) froma hard stop position associated with the hard stop.

At 96, the motor control module 14 and/or the boosting module 22 inexecuting the boost routine starts the electric motor 15 with anincreased or predetermined level of current (boost current level), whichprovides a boosted output torque.

At 98, the boosting module 22 may start a counter. At 100, the boostingmodule determines whether the counter has expired (i.e. exceeded apredetermined threshold). Task 102 may be performed when the counter hasexpired. Tasks 96-102 are performed to apply the boost current for ashort predetermined period (boost period) to break free the leadscrew 50and/or the rotor nut 54. The predetermined threshold and/or boost periodmay be set based on an amount of time that the leadscrew 50 and/or rotornut 54 were in a binded state. The predetermined threshold and/or boostperiod are set to assure that the binded state is overcome.

At 102, the force control module 28 decreases the current supplied tothe electric motor 15 to an applied current level providing an outputtoque that is less than the boosted output torque. The applied currentlevel is the current level used to grip (or hold) the object. Theboosting method may end at 104.

An example of a torque plot illustrating the boost mode is shown in FIG.5. In FIG. 5 a first torque level is shown for when the boost current issupplied and an applied torque is shown for when the applied currentlevel is supplied. The boost current level may be set at, for example, a100% output current level corresponding to a 100% output torque level ofthe electric motor 15, and/or may be set based on the applied currentlevel. The boost period may be set to ensure enough time to overcomebinds in worst case situations. The boost current level may be set to bea predetermined amount of current more than the applied current level toeffectively eliminate a bind. This ensures the force applied during anapplied torque mode (applied force) is not too large to prevent a bindcreated based on the applied force from being overcome during the boostmode.

Although the boost mode overcomes binded states of a motor, accountingfor binds and incorporating use of a boost mode can effectively decreaseusable force and stroke of the motor. Since an increased level of forceis needed to overcome a binded state created through the use of anapplied force, the applied force is set at a level that is less than amaximum output force level of the motor.

The boost mode is used when at a hard stop and when initiallytransitioning from an open state or from a closed state. The fingers 38are moved from a hard stop position to a non-binded position. As aresult, the stroke associated with the applied mode is decreased, sincethe fingers 38 are moved from the hard stop positions during the boostmode. Although the usable stroke is decreased, the amount of reductionis minimal, as the binded state is overcome when the fingers 38 or othergripper components are moved off the hard stop.

If the boost mode is activated while closing the fingers 38 to grip (orhold) an object, the object may be gripped with a maximum force, whichmay not be decreased when switching from the boost mode to the appliedcurrent mode. This not only applies too much force on the object, butalso creates a worst case binding condition, as the force applied on theobject is a maximum force. Thus, the object is not gripped during theboost mode, which reduces the usable stroke of the electric motor 15.

End-Of-Travel Move

Referring now also to FIG. 6, an end-of-travel routine is illustrated.The fingers 38 are shown during an open stroke, at a hard stop in afully open state (stall condition), and during a close stroke. Theend-of-travel module 23 may move the fingers 38 and/or other componentsof the holding device 16′ away from a hard stop to prevent binding. Theend-of-travel module 23 prevents binding by ensuring that the leadscrew50 does not remain in a hard stop position. As an example, an outerdiameter (OD) style gripper that applies a grip (or hold) force whenclosing fingers to grip an object does not need to remain on a hard stopwhen opening the fingers. Therefore, the end-of-travel module 23 maydetect a hard stop at the end of an open stroke and move the fingers 38and/or other components of the holding device 16′ away from the hardstop. The end-of-travel module 23 may detect the hard stop based on, forexample, the OPEN SENSE signal.

If the move away from the hard stop is done upon detecting the hardstop, binding does not occur and/or is minimized. The end-of-travelmodule 23 may move the fingers 38 and/or other components of the holdingdevice 16′ a predetermined distance (0.002 of an inch) away from thehard stop to prevent binding and minimize the amount of usable strokereduction.

The end-of-travel routine is not performed when gripping an object, butrather is used at an end of a transition from a grip or hold (e.g.,closed) state to a release (e.g., open) state. A movement of the fingers38 (e.g., 0.002 of an inch) off an object results in zero grip force.

The end-of-travel routine may be used in applications where the unitmovement is based on external hard stops and a pressing force is notneeded at the hard stops to grip an object. For these applications, theholding device 16′ simply provides enough force to overcome a non-bindedposition. An example application may include the use of the holdingdevice 16′ to push an object, as opposed to gripping an object. In theseapplications, the end-of-travel move from a hard stop may be used onboth open and close movements.

In FIG. 7, an end-of-travel method is shown. The end-of-travel methodmay be performed for gripping systems having a backdrivable leadscrew ora non-backdrivable leadscrew. Although the following tasks are primarilydescribed with respect to the implementations of FIGS. 1-2 and 6, thetasks may be easily modified to apply to other implementations of thepresent disclosure. The tasks may be iteratively performed. The methodmay begin at 110.

At 112, the end-of-travel module 23 and/or motor control module 14 maymove gripping elements from a hold (or grip) state to a release state.

At 114, the stall detection module 26 and/or the end-of-travel module 23may detect a hard stop at an end of a release stroke and subsequent toreleasing an object, as described herein.

At 116, the end-of-travel module 23 upon detecting the hard stop maymove the gripping elements from a current (or first) position to asecond position that is away from the hard stop. The second position maybe a predetermined distance from the first position (or hard stopposition).

At 117, the motor control module 14 maintains the gripping elements inthe second position. If the leadscrew is non-backdrivable, the motorcontrol module 14 may shut off the electric motor 15.

At 118, the holding device control module 12 and/or the motor controlmodule 14 may determine whether there is another object to grab and/ormay receive a request to grab a next object. Task 119 may be performedwhen there is another object to grab, otherwise the method may end at120.

At 119, the motor control module 14 moves the gripping elements from thesecond position to a third position to grip the next object. This mayoccur subsequent to the motor assembly 13 and the holding device 16being moved from a current position to a pick-up position. Subsequent totask 119, task 112 may be performed. Task 112 may be performed after themotor assembly 13 and the holding device 16 are moved from a current (orthe pick-up) position to a resultant (or drop off) position.

Hold Mode

As an alternative to using a non-backdrivable leadscrew, a backdrivableleadscrew may be used. Although backdrivable leadscrews do not havebinding issues associated with non-backdrivable leadscrews, backdrivableleadscrews can move when power is removed. For this reason, power is notremoved when using a backdrivable leadscrew to maintain a gripping forceon an object. This grip force may be maintained when the holding device16′ is at a hard stop.

Maintaining a motor current at high (gripping) levels for extendedperiods can quickly lead to heat issues within the motor 39. The motor39 may automatically shut off when temperature of the motor 39 exceeds apredetermined internal temperature (e.g., 85° C.). The motor 39 whenoperated at room or ambient temperature to produce an output torque ofgreater than or equal to a predetermined torque level (e.g., greaterthan or equal to 80% output torque) for extended periods can result intemperature of the motor exceeding the predetermined internaltemperature. This may result in the motor shutting off.

Referring now also to FIG. 8, a torque plot illustrating a hold mode isshown. The hold module 24 of FIG. 1 may reduce current to a motor 39 toprevent the temperature of the motor 39 from exceeding the predeterminedinternal temperature. The hold module 24 may reduce the current to themotor 39 from an applied force current during an applied torque mode toa hold current during a hold mode. The hold current may provide theoutput torque needed to maintain a grip on an object without droppingthe object. The current required to hold position of the leadscrew 50 isless than the amount of current to move the fingers 38 to a closed orgripping position. Thus, to minimize temperature of the motor 39 and toconserve energy, current to the motor 39 may be reduced after an objectis gripped while maintaining an adequate gripping force on the object.

The torque plot of FIG. 8 illustrates the boost mode, the applied torquemode and the hold mode. The boost mode may be used as described above tomove the fingers 38 and/or other components of the gripper off of a hardstop. After a predetermined period and/or after the fingers 38 havemoved a predetermined distance, the applied torque mode may then be usedto move the fingers 38 to a gripping position and grip the object. Theforce signal FORCE from the hold device control module 12 may indicatethe force, output torque and/or amount of current used during theapplied torque mode.

The hold module 24, upon detecting a stall condition, may then reducethe current to the electric motor 15 to provide a hold output torque andthus a hold force on the object. The hold current, hold output torqueand/or hold force may be predetermined and stored values stored in thememory 29. The hold module 24 may reduce the current to the electricmotor 15 by adjusting the force signal FORCE and/or by generating asecond force signal to be used during the hold mode. The force, outputtorque, and/or current used during the hold mode may be predeterminedand independent of the force, output torque, and/or current used duringthe applied torque mode. The stall condition may be detected asdescribed above.

The current commanded by the hold module 24 may be predetermined and setto ensure that a minimum force is maintained on the object to preventdropping of the object during the hold mode. The motor current isadjusted to and during the hold mode to maintain the motor 39 at thegripping position. The current level during the hold mode may be, forexample, half the current level during the applied torque mode, whilepositions of the finger 38 and/or the leadscrew 50 and grip force aremaintained. Although the current level to the electric motor 15 isreduced, the grip force during the hold mode may be equal to the gripforce during the applied torque mode.

In FIG. 9, a gripping method is shown. Although the following tasks areprimarily described with respect to the implementations of FIGS. 1-2 and8, the tasks may be easily modified to apply to other implementations ofthe present disclosure. The tasks may be iteratively performed. Themethod may begin at 130.

At 132, the boosting method is performed to move gripping elements froma hard stop and to grip and hold an object. A boost current level may beused to move the gripping elements from the hard stop. An appliedcurrent level may be used to move the gripping elements to a grippingposition. The boost current level may correspond to, for example, a 100%torque level of the electric motor 15. The applied current level maycorrespond to, for example, an 80% current level torque level of theelectric motor 15. At 134, the stall detection module 26 detects a stallcondition, as described herein.

At 136, the hold module 24 or the force control module 28 reducescurrent from the applied current level to a hold current level toprovide a hold force. The hold current level may correspond to, forexample, a 40% torque level of the electric motor 15. The hold force isgreater than a minimum force to hold the object. The method may end at138.

As an alternative, the above tasks may be modified to adjust pressuresof a regulator instead of adjusting current of an electric motor when apneumatically controlled holding or (gripper) system is used to providethe boost, applied, and hold force levels.

Force Adjustment

Pneumatic based gripper systems use a pressure regulator to reduceoutput force of a gripper. The pressure regulator regulates pressurewithin the gripper to prevent damage to gripper components. Instead ofusing a pressure regulator, the motor control module 14 and/or the forcecontrol module 28 provides the force signal FORCE to the motor 39 tocontrol force applied on an object via a force adjustment routine.

The motor 39 may have an analog input that receives the force signalFORCE. The force signal FORCE may be a control signal, an analog voltagesignal and/or an analog current signal that swings between, for example0 and a predetermined voltage and/or current level. Example swingvoltage ranges are 0-5 volts (V) and 0-10V. Example current swing rangesare 0-20 milli-amperes (mA) and 4-20 mA. The actual voltage and/orcurrent supplied to the electric motor 15 may be different than avoltage and/or current level of the force signal FORCE. The force signalFORCE may be at a minimum voltage and/or current level when a currentand/or voltage level supplied to the electric motor 15 is at a maximumvoltage and/or current level. The force signal FORCE may be at a maximumvoltage and/or current level when a current and/or voltage levelsupplied to the electric motor 15 is at a minimum voltage and/or currentlevel.

Referring now also to FIG. 10, an example force versus voltage graph ofa transfer function is shown. The motor 39 may provide a maximum outputforce (e.g., 200 lbs) when the voltage of the force signal FORCE is 0and a minimum output force (e.g., 100 lbs) when the voltage of the forcesignal FORCE is at a maximum (e.g., 10V). In the example shown, theminimum force is 50% of the maximum force. As the force signal FORCE isincreased from 0V to 10V output force of the motor 39 may linearlydecrease from the maximum force to the minimum force. The above-providedmaximum and minimum values are provided as an example and may vary basedon the mechanical and software implementation, the gripper applicationof use, the gripper motor, and/or the voltage and/or current settings inthe holding device control module 12 and/or motor control module 14.

The output force associated with the voltage range and/or current rangeof the force signal FORCE can be applied independently to both the openand close strokes of the holding device 16′. The voltage and currentranges may be predetermined during a setup procedure by first assigninga minimum torque (or force) value MIN and a maximum torque (or force)value MAX. The minimum and maximum torque values MIN, MAX may be storedin the memory 29 of the motor control module 14. The motor controlmodule 14 may then use a linear equation to interpolate and/or determinetorque values between the minimum and maximum torque values MIN, MAXbased on the voltage and/or current swing ranges. The voltage and/orcurrent swing ranges may be determined when setting up the holdingsystem 10 and/or the holding device 16′ and/or may be determined inreal-time during use of the holding device 16′. The voltage and/orcurrent swing ranges may be determined at any point in a cycle of agripping procedure.

In operation, the motor control module 14 may adjust the force signalFORCE based on the torque values set and determined during the setupprocedure. The maximum torque value MAX and/or values within apredetermined range of the maximum torque value MAX may be used during aboost mode. The torque values between the minimum and maximum toquevalues MIN, MAX may be used during the applied torque mode. The minimumtorque value MIN may be used during the hold mode. The holding devicecontrol module 12 and/or the motor control module 14 control the gripforce by adjusting the force signal FORCE. As an alternative, the gripforce may be controlled via an external potentiometer, which may beprovided as part of a user interface of the holding device controlmodule 12.

By using sensor(s) (e.g., encoder) internal to the motor 39 and byproviding feedback from those sensors to the motor control module 14,the above-described implementations provide flexible gripper system(s).The gripper system(s) may be adjusted via the motor control module 14 toaccommodate different applications and objects without changing grippermotors, cables, sensors, etc. The motor control module 14 may beprogrammed and reprogrammed based on the application of use. Voltage,current and/or output torque settings may be adjusted via a userinterface of the motor control module 14 to accommodate different sizedobjects and application forces.

In FIG. 11, a torque method is shown. Although the following tasks areprimarily described with respect to the implementations of FIGS. 1-2 and10, the tasks may be easily modified to apply to other implementationsof the present disclosure. The tasks may be iteratively performed. Themethod may begin at 140.

At 141, holding device control module 12, the force control module 28 orother control module determines a minimum output torque and a maximumoutput torque of the electric motor 15 is determined. These torquevalues may be stored in the memory 29.

At 142, the holding device control module 12, the force control module28 or other control module assigns a maximum voltage and/or current tothe minimum output torque for the force signal FORCE. At 143, theholding device control module 12, the force control module 28 or othercontrol module assigns a minimum voltage and/or current to the maximumoutput torque for the force signal FORCE.

At 144, the motor control module 14 interpolates output torques betweenthe minimum output torque and the maximum output torque based on theminimum voltage and/or current and the maximum voltage and/or current.

At 145, the force control module 28 operates the holding device 16 inthe applied torque mode based on the interpolated output torques. Theholding device 16 may be operated to perform a hold stroke to grip anobject or a release stroke to release the object when in the appliedtorque mode.

At 145, the hold module 24 may operate the holding device 16 to hold theobject by providing the minimum voltage and/or current in the forcesignal FORCE during the hold mode. The minimum voltage and/or currentmay be provided when the holding device 16 is in a stall condition. At146, the force control module may operate the holding device 16 torelease the object by providing a voltage and/or current (releasevoltage and/or release current) in the force signal FORCE that isgreater than the minimum voltage and/or current. The release voltageand/or current may be as high as the maximum voltage and/or current. Themethod may end at 147.

Cable Assembly

Referring now also to FIGS. 12A-12C, perspective views and pin outs ofthe cable assembly 20 is shown. The cable assembly 20 includes thesecond connector 19 that is connected to the holding device controlmodule 12 via the flex cable 17. The cable assembly 20 also includes thethird connector 32 and the fourth connector 33. The third and fourthconnectors 32, 33 may connect directly or indirectly to the motor 39.The third and fourth connectors 32, 33 are connected to the secondconnector 19 via a cable 149. The cable 149 includes the wires 30, 31.The cable assembly 20 allows power and signals provided to and receivedfrom the motor control module 14 to be provided via a single cable (i.e.the flex cable 17) this minimizes the interface between the holdingdevice control module 12 and the motor control module 14.

Although various pin assignments may be used, an example pin assignmentis shown. Each of the connectors 19, 32, 33 may include any number ofconnector pins and have any number of associated wires or signal lines,which are included in the cable 149. The number of pins in the secondconnector 19 may be equal to a sum of the number of pins in the thirdand fourth connectors 32, 33. The number of pins in the third and/orfourth connectors 32, 33 may be less than or equal to the number of pinsin corresponding connectors on the motor 39. Output pin assignments canbe adjusted in memory of the motor 39 and/or the holding device controlmodule 12. An example pin out of each of the connectors 19, 32, 33 isshown.

The second connector 19 may include a POWER, GROUND, OPEN, CLOSE, OPENSENSE, CLOSE SENSE, ANALOG FORCE and I/O POWER pins. The POWER andGROUND pins are connected to respective voltage and ground references.The signals on the OPEN, CLOSE, OPEN SENSE, and CLOSE SENSE pins may bediscrete I/O signals. The OPEN and CLOSE pins receive open and closecommand signals to command the motor 39 to transition between OPEN andCLOSE states (i.e. actuate the holding device 16′). Use of separate OPENand CLOSE pins and corresponding signals separating these signals andallow for a “do-nothing” state where neither signal is applied. The OPENand CLOSE pins may be referred to as HOLD and RELEASE pins.

The OPEN SENSE and CLOSE SENSE pins are used to feedback OPEN SENSE andCLOSE SENSE signals from the motor to the holding device control module12. The OPEN SENSE and CLOSE SENSE signals indicate when the holdingdevice 16′ has reached a hard stop while in an open or closed state. TheANALOG FORCE pin receives the force signal FORCE and is used to commandan output torque of the motor 39. This pinout may be used, for example,in direct current (DC) applications.

The I/O POWER pin may be used to supply power to the motor controlmodule 14 and/or logic devices (e.g., PNP transistors) within the motor39. The motor 39 may receive two power supply voltages; one forproviding power to the electric motor 15 and the other to provide powerto the motor control module 14 and/or logic devices. This allows theelectric motor 15 to be operated at a higher voltage than the motorcontrol module 14 and/or logic devices. The increased voltage suppliedto the electric motor 15 allows the electric motor 15 to be operated atincreased output speeds and/or provide increased output torque levels.As an example, the POWER pin maybe provided with 48V and the I/O POWERpin may be provided with 24V. Although the third connector 32 is shownas including the ANALOG FORCE pin, the third connector may alternativelyinclude the POWER pin.

In an alternative implementation, the I/O POWER pin is not included andthe electric motor 15 operates based on the same voltage supply as themotor control module 14 and/or logic devices. When the I/O POWER is notused, the power provided to the POWER pin may be spliced and provided tocorresponding POWER and I/O POWER pins in the third and fourthconnectors 32, 33. This reduces the first connector from an 8-pinconnector to a 7-pin connector. As an alternative to splicing power fromthe second connector 19 to the third and fourth connectors 32, 33, thesecond connector 19 may be an 8-pin connector and the holding devicecontrol module 12 may provide the same power to both the POWER and I/OPOWER pins of the second connector 19.

The cable 149 may be ‘Y’-shaped. Conductors of the cable 149 may beformed of, for example, gold (Au), nickel (Ni), brass, copper (Cu), zinc(Zn) and/or other electrically conductive materials. The cable 149 mayinclude wires as shown and may not include a ground shield and/orsheath.

The pinouts shown in FIGS. 12B-12C satisfies functionality requirementsof point-to-point (or hard stop-to-hard stop) applications. Hardstop-to-hard stop applications refer to applications when a gripper istransitioned iteratively between hard stops and provides force to graban object when at the hard stops.

The gripper implementations described above allows a gripper totransition to unknown (not predetermined or stored in memory) hard stopspositions while allowing an output force to be applied at the hard stoppositions. The motor control module of the gripper may be programmableto allow a manufacturer and/or a user to adjust various settingsdisclosed herein. The motor control module may be programmed to provideone or more of any of the above described features.

Referring now to FIGS. 13 and 14, a holding device 16″ is shown. Theholding device 16″ is a clamp and is attached to a motor 39′, which maybe similar to the motor 39. The motor 39′ includes a motor controlmodule 14′ that linearly actuates a leadscrew 50′. The holding device16″ includes an actuating arm 150, a link 152, a crank arm 154, and acrankshaft 156, which are in a clamp housing 157. The crankshaft 156 isconnected to a clamp arm 158 (or other tooling or gripping element).

In operation, the leadscrew 50′ is linearly actuated and received by theactuating arm 150. The actuating arm 150 is linearly actuated to movethe link 152 and rotate the crank arm 154 on the crankshaft 156. Therotational movement of the crankshaft 156 rotates the clamp arm 158 toapply pressure on and/or hold a part 160 on a fixture 162. The clamp arm158 may be attached to a toggle mechanism and/or links to lock to thepart 160. The motor 39′ and/or the holding device 16″ may hold the clamparm 158 in a locked state when electrical power is removed from themotor 39′. The clamp arm 158 is in a HOLD state when in contact with thepart 160 and is in a RELEASE state when not in contact with the part160. FIG. 13 shows the clamp arm 158 in the RELEASE state and FIG. 14shows the clamp arm 158 in the HOLD state.

The motor control module 14′ may operate the motor 39′ to actuate theclamp arm 158, as described above for the operation of the motor controlmodule 14 and the motor 39 in actuating the fingers 38 and with respectto the implementations of FIGS. 2-11. This includes detecting stallconditions, shutting off power to the motor 39′, boosting output torqueof the motor 39′, moving the clamp arm 158 away from the hard stop,reducing power during a hold mode, adjusting force output of the motor39′, etc.

In FIGS. 15-17, torque plots (or profiles) illustrating a move mode andmultiple applied modes and a gripping method are shown. The motorcontrol module of FIG. 1 may further include a move module 200. The movemodule may implement a move mode, examples of which are illustrated inFIGS. 15-17.

Although the following tasks are primarily described with respect to theimplementations of FIGS. 1-2 and 15-16, the tasks may be easily modifiedto apply to other implementations of the present disclosure. The tasksmay be iteratively performed and may be implemented in a holding system,such as in a gripping system or a clamping system. The method may beginat 208.

At 210, the boosting method is performed (the boost torque mode isactivated) to move gripping elements from a hard stop and to grip andhold an object. A predetermined boost current level may be used to movethe gripping elements from the hard stop. The predetermined boostcurrent level may correspond to, for example, a 100% torque level of theelectric motor 15. Subsequent to task 210, the holding system istransitioned from the boost torque mode to a move torque mode.

At 212, a move torque mode is activated via, for example, the movemodule 200. The move module 200 sets a predetermined move current levelfor the electric motor 15 to minimize resulting motor heat and thusincrease life of the electric motor 15. The predetermined move currentlevel may be used for a predetermined period. The allowed torque duringthe move mode is at a level to cycle or move the gripping elementsand/or a clamping arm reliably to a gripping position. The predeterminedmove current level may correspond to, for example, a 30% torque level ofthe electric motor 15 when gripping elements are being moved, as inFIGS. 2 and 6.

The predetermined move current level may be at, for example, a 60%torque level when moving a clamping arm, as in FIGS. 13 and 14. It isassumed for clamping applications that there is a tooling weight on anarm, which is being moved. Also, by keeping the move current level low(i.e. less than a predetermined level), an impact experienced at an endof a stroke will be minimized. Reducing this impact as well as theoverall motor heat maximizes longevity of the electric motor 15.

At 214, the end-of-travel module determines whether an end of a stroke(or end-of-travel) condition has been detected. Task 216 is performedwhen an end of a stroke has been detected. At 216, the applied torquemode may be activated and the move torque mode may be deactivated whenan end of a stroke is detected. A predetermined applied current levelmay be used to compress materials, components, and/or objects havingphysical compliance that are in a holding system, a gripper, a clamp,and/or a system and/or object being held. The compression is provided toadequately grip or hold the object. The compression may also be providedto remove, for example, gaps in the holding system, gripper, clamp,and/or system and object being held. The predetermined applied currentlevel may correspond to, for example, a 50-100% torque level of theelectric motor 15.

A predetermined length of the applied torque mode is set. As an example,in a gripper application, examples of which are provided above, thepredetermined length of the applied torque mode may be set to 50milliseconds (ms). As another example, in a clamp application, examplesof which are provided above, the predetermined length of the appliedtorque mode may be set to 175 ms.

In FIG. 15, the applied torque mode is shown as providing apredetermined applied current level of 100%. In other implementations,the amplitude of the predetermined applied current level may be based ona force adjustment routine, as described with respect to FIG. 10. FIG.16 shows resulting applied torque levels when using a 0-5V analog input.Subsequent to the applied torque mode, the torque (or current) controlalgorithm can then transition to operating in the hold torque mode.

At 216, the hold module 24 or the force control module 28 reducescurrent from the predetermined applied current level to a predeterminedhold current level to provide a hold force. The predetermined holdcurrent level may correspond to, for example, a 40% torque level of theelectric motor 15. The hold force is greater than a minimum force tohold the object. The method may end at 220.

Although the terms first, second, third, etc. may be used herein todescribe various voltages, currents, elements, modules, signals, and/orconnectors, these items should not be limited by these terms. Theseterms may be only used to distinguish one item from another item. Termssuch as “first,” “second,” and other numerical terms when used herein donot imply a sequence or order unless clearly indicated by the context.Thus, a first item discussed herein could be termed a second itemwithout departing from the teachings of the example implementations.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. For purposes of clarity, thesame reference numbers will be used in the drawings to identify similarelements. As used herein, the phrase at least one of A, B, and C shouldbe construed to mean a logical (A or B or C), using a non-exclusivelogical OR. It should be understood that one or more steps within amethod may be executed in different order (or concurrently) withoutaltering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable hardware components that provide the described functionality;or a combination of some or all of the above, such as in asystem-on-chip. The term module may include memory (shared, dedicated,or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors. In addition, some or all code from a single module may bestored using a group of memories.

The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, the specification, and the following claims.

What is claimed is:
 1. A holding system comprising: a holding devicecontrol module configured to (i) provide a power output and (ii)generate an open signal, a close signal, and a force signal, wherein theforce signal indicates a requested output torque of an electric motor; amotor control module configured to generate feedback signals indicatinga stall condition of a holding device, wherein the feedback signals aregenerated by a sensor mounted within a housing of the electric motor;and a cable assembly comprising: a first connector configured to connectto the holding device control module via a cable, wherein the cable isconnected between the holding device control module and the cableassembly, a second connector connected to the motor control module andproviding the open signal and the close signal from the holding devicecontrol module to the motor control module, wherein the second connectorprovides the feedback signals from the motor control module to theholding device control module, a third connector connected to the motorcontrol module and providing the power output or the force signal fromthe holding device control module to the motor control module, andsignal lines separate from the cable assembly and connected between the(i) first connector and (ii) at least one of the second connector andthe third connector.
 2. The holding system of claim 1, wherein thesignal lines comprise: a first set of lines connected between the firstconnector and the second connector; and a second set of lines connectedbetween the first connector and the third connector.
 3. The holdingsystem of claim 1, wherein gripping elements of the holding device arenot moving when in the stall condition.
 4. The holding system of claim1, wherein a component of the holding device is against a hard stop andis not moving when in the stall condition.
 5. The holding system ofclaim 1, wherein the second connector provides a first signal and asecond signal from the motor control module to the holding devicecontrol module, wherein the first signal indicates when the holdingdevice has reached a hard stop while in an open state, and wherein thesecond signal indicates when the holding device has reached a hard stopwhile in a closed state.
 6. The holding system of claim 1, wherein: thesecond connector provides a power signal from the holding device controlmodule to the motor control module; the power output is at a firstvoltage; the power signal is at a second voltage; the second voltage isless than the first voltage; the second connector provides the poweroutput to the motor control module to supply power to the electricmotor; and the second connector provides the power signal to power themotor control module.
 7. The holding system of claim 1, wherein thesecond connector provides the power output from the holding devicecontrol module to the motor control module.
 8. The holding system ofclaim 1, wherein: the second connector receives a first portion of thepower output from the first connector and provides the first portion ofthe power output from the holding device control module to the motorcontrol module to power the electric motor; and the third connectorreceives a second portion of the power output from the first connectorand provides the second portion of the power output from the holdingdevice control module to the motor control module to power the motorcontrol module.
 9. The holding system of claim 1, wherein the thirdconnector provides the force signal from the holding device controlmodule to the motor control module.
 10. The holding system of claim 1,wherein: the first connector provides a first portion of the poweroutput to a first pin of the second connector; the first connectorprovides a second portion of the power output to a second pin of thesecond connector; the second connector provides the first portion of thepower output to the motor control module to power the electric motor;and the second connector provides the first portion of the power outputto the motor control module to power the motor control module.